docs: polish README (hero, badges, emoji sections, panel preview)

[abruption]

Make the README more presentable like the reference project (skainguyen1412/antigravity-usage):

• centered hero: title + shields badges (npm version/downloads, CI, node, license) + tagline + attribution
• a rendered /usage panel preview as a code block
• emoji section headings, cleaner structure
• keep existing technical content (install, cross-platform table, HTTP endpoint, dev/release, notes)

Closes via docs PR.